So let’s begin with growth hormone targeting your adipose tissue. And when growth hormone targets adipose tissue, this causes lipolysis. You know our two products of lipolysis are glycerol and fatty acids. The glycerol can go into the liver and be converted to glucose.
And then that glucose from the liver can go into circulation, so we will increase our glucose concentration in the circulation.
Remember, one of the stimuli for synthesizing and secreting growth hormone was a low plasma glucose concentration. So in this case, we’ve elevated our glucose concentration. Now the fatty acids can also enter into circulation, and this will increase our plasma level of our fatty acids as well. Now growth hormone can also target a lot of other types of tissues. And when it does target these tissues, it decreases glucose utilization.
So if we decrease glucose utilization by the cells, meaning the cells are not going to be using up that glucose, then your glucose level in the circulation can remain elevated. So what this does then, if we have increased plasma glucose and increased fatty acid levels in the plasma as well, these can all provide the energy that’s needed for growth.
So we’re going to begin with the insulin-like growth factor that was synthesized and secreted by the liver. Insulin-like growth factor, once it’s synthesized and secreted, will have a negative effect on the anterior pituitary. Specifically, what it does is it inhibits the responsiveness for growth hormone releasing hormone.
So if I inhibiting the responsiveness for growth hormone releasing hormone on the endocrine cells, then those endocrine cells will not synthesize and secrete growth hormone. Insulin-like growth factor one can also act on the hypothalamus and have a negative impact on the hypothalamus as well, because it will inhibit secretion of growth hormone releasing hormone. Again, IGF-1, insulin like growth factor, inhibits secretion of growth hormone releasing hormone from the hypothalamus. So if we don’t release growth hormone releasing hormone from the hypothalamus, then you cannot stimulate the anterior pituitary to synthesize and secrete growth hormone. So in essence, we’ve stopped the synthesis and secretion of growth hormone.
There’s also another hormone synthesized and secreted by the hypothalamus that can help turn off secretion of growth hormone, and this is called growth hormone inhibiting hormone.
So the neurosecretory neurons in the hypothalamus can also synthesize and secrete growth hormone inhibiting hormone: GHIH. So if growth hormone inhibiting hormone is synthesized and secreted, it inhibits the anterior pituitary from synthesizing and secreting growth hormone. So we have two ways in which we can turn off growth hormone synthesis and secretion. One of those involves the negative feedback loop, utilizing insulin-like growth factor one.
The other is by synthesizing and secreting growth hormone inhibiting hormone..